1. Field of Invention
The present invention pertains to the art of refrigerated appliances and, more particularly, to a refrigerator having an adaptive defrost cycle wherein the defrost cycle is operated during periods of low use as determined by a controller upon receiving signals representative of door opening patterns.
2. Discussion of Prior Art
Refrigerated appliances, for both commercial and domestic applications, utilize a refrigeration system typically including, but not limited to, a compressor, a condenser and an evaporator. During operation, water vapor condenses on the evaporator and may freeze. The ensuing ice or frost accumulation significantly reduces the amount of air which can flow through the evaporator unit resulting in a diminished capacity to cool the appliance efficiently. In order to reduce the effects of frost build-up on the evaporator, refrigerated appliances often incorporate a operating cycle designed to periodically defrost the evaporator, thereby renewing the evaporator""s ability to operate efficiently.
Early defrost cycles simply de-activated the refrigeration system for a period of time so that temperature of the unit would rise and the frost build up would melt away. However, this method required substantial time and could cause the temperature in the appliance to rise to the point that food contained therein would be damaged. Later appliances incorporated a defrost heater mounted adjacent to the evaporator which, when operated, would hasten the process and thereby reduce the impact on internal appliance temperatures. Once a shorter defrost cycle was developed, determining the optimal time to operate the cycle, and reducing the impact on food contained within the appliance became important.
There are various methods utilized to determine the best time to operate defrost cycles. For example, manufactures have provided sensors mounted to the evaporator to provide an indication of frost accumulation, or a controller is provided to count the operating hours of the compressor such that the defrost cycle was activated when a pre-determined time period was achieved. Other methods include load monitors to determine periods of reduced energy consumption to provide an indication of low use. However, this method would not account for leaks in the system or other anomalies that provided a false indication of low usage. The prior art also discloses the use of sensors to monitor and count an opening condition of a door to provide an indication of a cooling load required by the appliance. While there exist many methods of determining an appropriate time to activate the defrost cycle, there still exists an need for controller that can determine actual periods of low usage such that the defrost cycle is operated at times which have the least impact on food articles stored in the refrigerator.
A refrigerated appliance constructed in accordance with the present invention includes, in addition to an overall refrigeration system, a controller, at least one door sensor which provides signals indicative of opening conditions of a door of the appliance and a memory for storing the signals. The controller groups the signals stored in the memory into usage blocks. For instance, each hour of a day has a designated usage block which is further grouped into periods of low use and high use. When a defrost condition is indicated, the controller looks to activate the defrost system during periods of low use, preferably during the period of least usage.
In accordance with another aspect of the invention, a stirring fan mounted within a fresh food compartment is operated continuously during the defrost cycle to re-circulate cooling air throughout the compartment such that the temperature of the food contained within the compartment is not adversely affected.
In accordance with another aspect of the invention, the controller will lower the temperature set point of the freezer compartment prior to activation of the defrost system. In this manner, temperature loss during the defrost cycle will not cause the temperature of the freezer compartment to rise above the temperature set point, which could adversely impact the food contained therein.
Finally, the control will determine the optimal interval between successive defrost cycles, as well as the duration of each defrost cycle, based upon previously completed cycles. The controller stores in memory information relating to the time duration and interval between each prior defrost. If the previous cycle was shorter than a predetermined period, thus indicating that frost build-up was minimal, the controller will allow a longer interval between successive activations of the defrost system. In this manner, the controller can optimize the defrost operation such that food within the system is not subject to constant temperature variations.
In any event, additional objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention, when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views.